Cavity resonator circuit



Dec. 20, 1955 B. WISE 2,727,950

CAVITY RESONATOR CIRCUIT Filed NOV. 28, 1952 3 Sheets-Sheet l 00 73 4/ 7' CW V/ 7/ our/907' //YPU7' BEHNHRD WISE- INVENTOR.

ATTORNEY Dec. 20, 1955 s. WISE 2,727,950

CAVITY RESONATOR CIRCUIT Filed Nov. 28, 1952 s Sheets-Sheet 2 INVENTOR.

BERNHRD WISE JTTORNEY Dec. 20, 1955 B. WISE CAVITY RESONATOR CIRCUIT 3 Sheets-Sheet 3 Filed Nov. 28, 1952 INVENTOR. BE RNHRD WISE- MH-M k United States Patent- CAVITY RESONATOR CIRCUIT Bernard Wise, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application November 28, 1952, Serial N 322,909

8 Claims. (Cl. 179-171) This invention relates generally to electron discharge device circuits employing cavity resonators in association therewith, and particularly to rectangular cavity resonator circuits tunable over an extended frequency range, such as 4 or :1.

It is an object of this invention to provide an improved ultrahigh frequency cavity resonator for use in association with electron discharge devices.

Another object of this invention is to extend the tuning range of rectangular type cavity resonators used in conjunction with an electron discharge device and still maintain the size of the resonator within a restricted volume.

A further object of this invention is to simplify tuning, coupling and neutralization of ultrahigh frequency cavity resonators.

Still another object of this invention is to enable the operation of a cavity resonatorcircuit efiiciently in either of two difierent modes of operation.

in accordance with this invention, a cavity resonator circuit arrangement is provided which is adapted to be used with concentrically constructed vacuum tube electron discharge devices (that is, where the vacuum tube elements are brought out of the vacuum .tube to circular or cylindrical terminals spaced .apart but arranged on a common axis).

Two separate resonant cavities are used in connection with a single vacuum tube. A first cavity, which shall be termed the input cavity, acts as a resonant circuit between two of the vacuum tube terminals, for example, the cathode and control grid. The second cavity, termed an output cavity, is coupled between two of the vacuum tube terminals, at least one of which is difierent from the first set of terminals used, for example, between the anode and the control grid. An important feature is the construction and arrangement of specially located blocks of conductive material placed in one or both of the two cavities to alter the electric field distribution within the cavity and eifectively increase .the electrical length thereof. The result of including these blocks of conductive material inside the cavity resonator, together with the positioning of the vacuum tube electron discharge device is to allow the cavity resonator to be tuned to resonance over a wide band of frequencies of the order of 4 or 5:1, and further to enable resonant operation of the cavity either in a first order mode, such as the TEm mode, or a third order mode, such as the T1330 mode.

An advantage of the rectangular cavity resonator circuit arrangement thus provided is that an increased area is available close to the vacuum tube electron discharge device for coupling energy into the input cavity resonator to excite the vacuum tube or for extracting energy from the output resonator. Furthermore, due to the particular arrangement of the blocks, the field distribution within the cavity resonator is such that neutralization from input to output can also be accomplished in the same portion of the resonator used for input and output coupling.

Another advantage of the circuit arrangement of this ice invention is that, due to the large frequency rangeover which the input circuit is tunable, the cavity resonator circuit may be operated as a frequency doubling circuit or as an intermediate power amplifier or power amplifier. For television application in the presently assigned ultra high frequency range from 470 to 890 megacycles, the input circuit can be tuned to resonance at any frequency in the band from 235 to 890 'megacycles. This wide tuning range ofiers the utility in television transmitter design that identical circuit elements and vacuum tubes may be employed in each of two separate stages, that is, a frequency doubler stage and a power amplifier stage. The use of identical circuit elements and tubes simplifies the parts replacement problem and circuit maintenance operations.

A more detailed description of the invention follows in conjunction with the accompanying drawing, wherein:

Fig. l is a longitudinal cross section in elevation of a cavity resonator circuit arrangement in conjunction with an electron discharge device embodying the invention. Fig. l is also a cross-sectional view of the cavity resonator of Fig. 3 taken along the line 1-1 thereof;

Fig. '2 is a transverse cross section in elevation of the device shown in Fig. 1 taken at right angles to the section shown in Fig. 1 along line 2-2. Fig. 2 is also a section alongline 22 of Fig. 3;

Fig. 3 is a top plan view of the cavity resonator system of Fig. 'l with the top cover removed taken along the line 33;

Fig. 4 is a top plan view in section of the same device along the line 44 ofFig. 1;

Figs. 5 and 6 show fragmentary plan and elevation in section views respectively of a portion of the cavity resonator device of the invention including a modification relating to the output coupling arrangement; and

Figs. 7 and 8 show fragmentary plan and elevation in section views respectively of a portion of the cavity resonator device of the invention including a modification relating to the neutralizing arrangement.

Referring to Fig. 1, there is shown an electron discharge device or vacuum tube 11 having an anode terminal .13, a control grid terminal 15 and a cathode terminal 17. The cavity resonator structure includes tuned input and output cavity resonator circuits for the vacuum tube discharge device 11. The input and output cavities are both rectangular in shape with the vacuum discharge device 11 centrally seated therein and extending through registered apertures in the cavity walls at the center of each cavity. These two cavities are defined by three flat walls. The input cavity 21 is contained between a first or cathode wall 23 and an intermediate or grid wall 25. The output cavity 27 is formed between the intermediate or grid Wall and a third or anode wall 29. The input cavity 21 is closed at its ends remote from the vacuum tube 11 by shorting bars 31. A similar set of shorting bars 33 closes the ends of the output cavity 27.

An anode spirally wound, spring-type contacting ring 35 is maintained in insulated relationship to the third or anode wall 29 by dielectric spacers 36 and 37, but is mechanically secured to the anode wall by a hold-down ring 38. The insulating spacers 36 and 37 perform the function of direct current isolation for the high anode voltage and further form a bypass circuit for radio frequencies between the anode contacting ring 35 and the anode wall 29.

A grid terminal spirally wound spring-type contacting ring 39 is carried by a rectangular metallic block 41 which is positioned in the output cavity. The rectangular metallic block 41 has a cylindrical aperture therein in register with the apertures in the walls 25, 29 to receive the vacuum tube 11 and is secured to the intermediate or grid wall by a pair of oppositely disposed clamps 43. The rectangular block 41 is maintained in insulated relationship to the intermediate. wall 25 and the clamps 43 by dielectric spacers 45, 47. The insulating dielectric spacers 45, 47 provide for direct current isolation for the grid of the vacuum tube 11 and form a radio frequency bypass circuit between the grid termi nal contacting ring 39 and the intermediate grid wall 25. For a vacuum tube discharge device 11 having a coaxial cathode and heater terminal arrangement, a cathode terminal spirally wound spring-type contacting ring 51 is carried within a cylindrical block 53. The cathode terminal block 53 has an integral flange 55 thereon for mechanically securing the block 53 and cathode terminal contacting ring 51 to the resonator structure. Like the dielectric spacers 36, 37, and 47, dielectric spacers 57 and 59 isolate the cathode for direct current potentials but form a radio frequency bypass circuit between the cathode terminal contacting ring 51 and the first or cathode wall 23.

With coaxial type heater-cathode terminals, the cathode terminal 17 is internally connected within the vacuum tube to one end of the heater filament, and the other end of the heater filament is brought out to a pin 61 contained coaxial with the cylindrical cathode terminal 17. A jack terminal 63 mechanically and electrically engages the heater terminal 61 to supply the heater current to the discharge device 11. A cathode and heater lead 65 is electrically connected to the cathode block 53 and a heater lead 67 is electrically connected to the heater jack terminal 63.

A pair of metallic blocks 71, 72 are positioned in the input cavity 21 in close proximity to the terminals of the vacuum tube 11. These metallic blocks 71, 72 are mechanically and electrically connected to the first or cathode wall 23 and effectively form a very low impedance line section between the vacuum tube terminals and the remainder of the input cavity 21. This very low impedance line section formed between the blocks 71, 72 and the adjacent intermediate or grid wall 25 acts to increase the electrical length between the electrodes of the vacuum tube 11 and the shorting bars 31. 'Provision of the blocks 71 and 72 forming the low impedance line section in the input cavity 21 has several highly beneficial results. The lower frequency limit to which the input cavity resonator 21 can be tuned is greatly extended because of the increase in effective electrical length of the input cavity 21. By choosing the blocks of the proper size and properly determining their position with respect to the vacuum tube 11, the input cavity 21 may be operated at three-quarter wave resonance, that is, the TE30 mode, over a wide range of frequencies. Therefore, the size of the cavity required to tune over a very wide frequency spectrum is greatly reduced by virtue of the fact that the cavity can be efficiently operated in either a quarter or three-quarter wave mode of operation.

The rectangular metallic block 41 in the output cavity 27 forms a short section of low impedance line which increases the effective electrical length of the output cavity 27. This low impedance line section is in the closely spaced portion between the block 41 and the third or anode wall 29. By making the physically long distance between the output terminals of the vacuum tube 11 electrically a longer distance, the quarter wave point for the lowest frequency at which the cavity resonator system can be operated is moved closer to the vacuum tube terminals. This arrangement also has the resultant advantage that the shorting bars 33 from the output cavity 27 will tune the output cavity to quarter wave resonance at a higher frequency. Thus the presence of the low impedance line section etfectively extends the tuning range both at the low and high frequencies.

The blocks 71, 72 in the input cavity and the rectangular block 41 in the output cavity are shown in the drawings as occupying the major portion of the spacing between the walls of the cavity with which they are associated. Although blocks of lesser thickness would act to some extent to load the cavity in the vicinity of the vacuum tube 11, as a practical matter the blocks 41, 71 and 72 should have a thickness more than onehalf of the distance between the walls to give a reasonable amount of loading.

Input and output coupling Referring now to Fig. 1 and also to Fig. 2, which is a cross section in elevation of the same device shown in Fig. 1 taken along the center line thereof in a direction transverse to the view of Fig. 1, there is shown a means for coupling radio frequency energy into the input cavity 21 and out of the output cavity 27, as well as an arrangement for providing neutralization when the cavity resonator circuit of this invention is used as a radio frequency amplifier.

The radio frequency input is through a short section of coaxial line having a cylindrical outer conductor 73 electrically and mechanically connected to the first or cathode wall 23 and an inner conductor 74 which extends through an aperture in the first or cathode wall 23 and terminates in a disc 75 in closely spaced capacitive relation to the intermediate or grid wall 25. If direct current isolation is desired between the inner conductor 74 of the radio frequency input line and the intermediate wall 25, a small piece of dielectric material 77 may be placed on the disc 75. This input coupling arrangement, including the coaxial line 73, 74 and the disc 75, electrostatically couples the radio frequency energy between the first or cathode wall 23 and the intermediate or grid wall 25.

The arrangement for extracting energy from the output cavity 27 is similar to the input coupling just described and includes a coaxial output line 81, 83 having its outer conductor 81 electrically and mechanically connected to the anode wall 29 and its inner conductor 83 terminated in a disc 85. The disc 85 may be provided with a piece of dielectric material 87 on one face to afford direct current isolation of the inner conductor 83 from the grid wall 25.

When the input cavity 21 and output cavity 27 are excited with radio frequency energy, transverse electric waves are set up in the lonigtudinal' direction, that is, between the shorting blocks 31 in the input cavity 21 and between the shorting blocks 33 in the output cavity 27. These lonigtudinal waves are in the plane of the drawing in Fig. 1 and perpendicular to the plane of the section in Fig. 2. The length of the input cavity 21 is such that from the vacuum tube electrodes inside the vacuum tube 11 to the shorting blocks 31 is one-quarter wavelength for operation over a large portion of the frequency band desired. However, the design of the input cavity with the metallic blocks 71 and 72 is such that the input cavity may be operated in the three-quarter wave mode over a wide range of the frequency spectrum desired. When the input cavity 21 is operated at three-quarter wave resonance, that is, the TE30 mode, the conductive blocks 71 and 72 forming the low impedance line section are outside the first quarter wave point. Starting at the tube electrodes inside the vacuum tube 11, the metallic blocks 71, 72 are outside the first quarter wave point of the standing wave of voltage for the resonant frequency, that is, more than one-quarter, but less than one-half, wavelength at the operating frequency from the vacuum tube electrodes.

In the input cavity 21, the input coupling arrangement consisting of the coaxial line section 73, 74 and the disc 75 couples energy directly into the cavity. Theoretically, this coupling point exists in the cavity at a point at which the resonator is effectively beyond cutoff. However, practically, the input cavity 21 is designed so that the attenuation is not sufficient to prevent setting up the desired order mode in the lonigtudinal direction and to permit its being propagated in the transverse direction. Therefore, the

signal will be developed across the vacuum tube electrodes. The cavity design is-influenced, as will beeX- plained later, by the electrical length that it represents in the transverse direction to the T1330 mode for proper neutralization.

in the output cavity 27, the output coupling arrangement 81, 83, 85 extracts energy from the lonigtudinal field. This lonigtudinal field is greatest in close proximity to the rectangular metallic block 41, that is, nearest the vacuum tube terminals. The greatest output coupling could be had by positioning the output coupling arrangement 81, 33, 85 immediately over the rectangular metallic block 41. However, sufiicient coupling is achieved at practically all frequencies by the arrangement of Fig. 2. One workable alternative system for increasing the amount of output coupling obtainable is described below in connection with Fig. 5.

A neutralizing probe 91 couples energy from the output cavity 27 back to the input cavity 21. The neutralizing probe 91 is electrically and mechanically connected to the anode wall 29 by metallic retaining nuts 93. The neutralizin probe 91 passes through an aperture 95 in the intermediate or grid wall 25 and terminates in a disc 97 in the input cavity 21. The degree of penetration of the neutralizing probe 91 into the input cavity 21 is made adjustable, for example, by providing screw threads 99 to engage the retaining nuts 93 to allow the degree of neutralization, that is, ne ative feedback, to be adjusted.

in Fig. 3 a top plan view of the device of Fig. 1 shows in detail the output cavity 27 with the third or anode wall 29 removed as indicated along the line 3 of Fig. 1. In this figure, the relative positions of the output coupling arrangement, including the disc 85 and the inner conductor 83 of the output line relative to the rectangular metallic block 41, are readily apparent. The position of the neutralizing probe 91 can also be seen. One form of mechanism for adjusting the position of the shorting bars 33 with respect to the position of the vacuum tube is shown, and includes two threaded shafts 101 and 103 which are threaded in reverse sense to each other, that is, one end (for example, the right-hand end) will have a right-hand thread whereas the other end (the left-hand end) will have a left-hand thread. As the shaft 101 or 103 is rotated, the shorting bars 33 are advanced toward or away from the center of the cavity at the same rate. An extension of the shaft 101 carries thereon a pinion 105. A similar pinion 106 is secured to the other shaft 103 and a sprocket chain 1317 mechanically links the two pinions 185 and 1% to rotate together. A knob 108, also secured to one of the shafts 1511 as an axle, is provided for conveniently rotating the shaft 191 to thereby adjust the positions of the shorting bars 33 in the output cavity 27.

Spirally wound contacting springs 169 are carried in a channel in the shorting bars 33 to establish electrical contact between the shorting bars 33 and the two plates 25 and 29 forming the intermediate and anode walls of the output cavity 27. These same springs 109 may be seen in section and in elevation by reference to Figs. 1 and 2.

Referring now to Fig. 4, there is shown a top plan view of the input cavity 21 as indicated along the line 44 of Fig. 1. The relative positions of the input coupling arran ement in plan are shown including the disc 75 and the inner conductor 74 of the output line. This figure also shows one form of mechanism for adjusting the position of the shorting bars 31 in the input cavity, and like that explained above in conjunction with the output cavity, has a pair of threaded shafts 111, 113 which engage threaded holes in the shorting bars 31. The two ends of the threaded shafts 111, 113 are threaded in reverse sense to each other so that as both are rotated in the same direction the shorting bars 31 are moved toward or away from the vacuum tube in the center of the cavity at the same rate. One of the threaded shafts 113 carries thereon a pinion 115. A similar pinion 116 is secured to the other shaft 111, and a sprocket chain 117 mechanically links the two pinions 115 and 116 so that they rotate together. A knob 118 is also provided to rotate the two shafts 111, 113 to adjust the position of the shorting bars 31.

Spirally wound contacting springs 119 in a channel or recess in the shorting bars 31 establish electrical contact between the shorting bars and the two plates 23 and 25 forming the cathode and intermediate walls of the intermediate cavity 21. These contacting springs 119 may also be seen in section in Fig. 1 and in elevation in Fig. 2.

Referring now to Figs. 5 and 6, there are shown fragmentary plan and elevation in section views respectively of a portion of the cavity resonator device of this invention including a modification relating to the output coupling arrangement. The modification includes a LJ-shaped metallic shim 121 electrically and mechanically secured to the rectangular metallic block 41 in the output cavity. This U-shaped shim 121 provides additional coupling for the longitudinal field existing within the cavity to the output coupling arrangement 83, 85.

Effectively, the metallic shim 121 acts to couple energy from the longitudinal field, which is very strong at the metallic block 41, to the output coupling arrangement 83, in a portion of the longitudinal field which would otherwise be weaker than is desirable for optimum output coupling.

Fig. 6 shows that the relative position of the shim 121 between the walls of the output cavity is near the center thereof, but preferably closer to the disc 35. This output coupling modification is especially useful at the higher end of the band of frequencies to which the output cavity H resonator is tunable.

In Fig. 7 there is shown a top plan view of a frag? ment of the input cavity 21 containin a modification re lating to the neutralizing probe 91; and in Fig. 8 there is shown a fragment of a cross section in elevation along the line 8 of the modification of the device shown in Fig. 7. A c -shaped metallic shim 123 is bridged across Inetallic blocks 71, 72 in the input cavity and is mechanically and electrically secured thereto. A reference to Fig. 8 will show the position of the U-shaped metallic shim 123 relative to the first or cathode wall 23 and the intermediate or grid wall 25. The U-shaped metallic shim 123 bridging the blocks 71, 72 in the input cavity acts to couple energy from the neutralizing probe 91 and disc 97 into the longitudinal field in the input cavity 21, The U-shaped metallic shim 123 has the closed portion of the U in close proximity to the neutralizing probe 91 or it may actually include the probe 91 inside the U.

Frequency doubler operation When operating the cavity resonator circuit of this invention as a frequency doubler in conjunction with a concentrically constructed vacuum tube electron discharge device 11, the input cavity 21 between the grid terminal contacting ring 39 and the cathode terminal contacting ring 51 is tuned to resonance at one-half the desired output frequency. For ultrahigh frequency television transmission, this input frequency will be between 235 and 445 megacycles. The short-circuiting bars 31 are adjusted so that the rst quarter-wave point away from the tube electrodes occurs at the short-circuitiug bars 31. Stated in another way, the input stage in doubler operation is operated in the TEio mode.

The output stage in doubler operation, this is, the cavity 27 between the control grid contacting ring 39 and the anode contacting ring 35, is tuned to the desired output frequency by positioning the shorting bars 33 at the first quarter-Wave point from the tube electrodes. For ultrahigh frequency television, this frequency will be between 470 and 890 megacycles. Due to the physical and electrical arrangement of the cavity, the input circuit in doubler operation will not support a three-quarter wave mode, that is, a 'IEao mode, as an integral multiple of the input frequency. This is due to the fact that, with the dimensions of the cavity and the blocks 71, 72 in the input cavity, the length of the input cavity is not the proper value to support the three-quarter wave mode of operation for any multiple of the input frequency. Because the input and output circuits are tuned to different frequencies of operation and because the input circuit will not support resonant operation of any multiple of the input frequency, no neutralizing arrangement is necessary for doubler operation, nor is any employed. In practice, the neutralizing control 91, 97 between the input and output cavities is simply removed from the cavity resonator system.

Power amplifier operation When the cavity resonator circuit arrangement of this invention is operated as a radio frequency power amplifier in conjunction with a concentrically constructed vacuum tube electron discharge device, the input cavity 21 between the grid terminal contacting ring 39 and the cathode terminal contacting ring 51 is tuned to resonance at the three-quarter wave mode, or TE30 mode. As explained above, the position of the blocks 1'1, 72 in the input cavity 21 for three-quarter wave operation is such that the blocks 71, 72 are outside the first quarter wavelength point, that is, more than one-quarter wavelength and less than one-half wavelength at the operating frequency from the tube electrodes.

The output stage is operated at one-quarter wave resonance in the same manner as the output stage in frequency doubler operation. In radio frequency power amplification, where both the input and output circuits contain resonant elements tuned to the same frequency and having a large value of Q, care must be taken to insure that sufficient neutralization is provided to prevent the stage from going into oscillation. Neutralization depends upon coupling a certain portion of energy back into the input cavity in opposite phase (180 out of phase) to that fed back through the interelectrode capacitances.

Neutralization The neutralizing probe 91, 97 in the cavity resonator circuit of this invention couples back a portion of the energy in the output circuit cavity 27 to the input circuit cavity 21 in the proper phase to effect the necessary cancellation. With the blocks as shown in the input cavity circuit, and the existence of a three-quarter wave mode of operation in the longitudinal direction of the cavity, that is, between the movable shorting bars 31, a three-quarter wave mode will also exist in the transverse direction. The energy in this transversely propagated field in the input cavity at the point at which the neutralizing control is located is 180 out of phase with the energy appearing between the input electrodes of the vacuum tube 11. In the output cavity 27, the energy appearing in the vicinity of the neutralizing control probe 91, 97 will be in phase with that between the electrodes of the vacuum tube since output cavity operation is in the first quarter wavelength. The neutralizing control 91, 97 picks up energy from the longitudinal field of the output cavity 27 and reinjects this energy into the transverse field in the input cavity 21 so that it appears 180 out of phase at the input electrodes of the vacuum tube 11. The degree of penetration of the neutralizing control 91, 97 into the input cavity determines the amount of energy coupled back from the output cavity to the input cavity.

When utilizing this neutralization arrangement, that is, coupling the energy fed back to a transversely propagated field so that it arrives in the proper phase at the vacuum tube electrodes, a caveat must be observed. At lower frequencies, the transverse dimension of the input cavity 21 may become too small to support the transverse three-quarter wave mode. Considering the resonant cavity as a shorted waveguide section loaded at its center, the waveguide'section will have a certain lower frequency limit below which the transverse wave will not be supported. By loading the waveguide at the center an additional amount, the transverse propagation can be supported at lower frequencies. This is most easily done by making the length of the blocks 71, 72 longer in the transverse direction, that is, in the direction transverse to the longitudinal direction of the input cavity which extends between shorting bars 31, 31. Making the blocks 71, 72 longer in the transverse direction has little or no effect on the operation of the input cavity 21 in the longitudinal mode.

If the blocks 71, 72 can not be made sufliciently long to support the desired transverse propagation down to the lower end of the frequency range desired with the transverse dimensions of the cavity chosen, the neutralizing probe 91, 97 can still be used, but the excitation is applied in the input cavity to the longitudinal field instead of the transverse field. Since the blocks are outside of the first quarter-wave point in the longitudinal field, if the energy extracted by the neutralizing probe from the output circuit is inserted into the longitudinal field at the blocks in the input circuit, it will be in the proper phase to furnish negative feedback or neutralization at the vacuum tube electrodes.

A mechanically simple but electrically efiective way to accomplish this feedback into the longitudinal field is to add a U-shaped shim 123 described in Figs. 7 and 8 which bridges the ends of the two blocks and is in close proximity to the neutralizing probe 91, 97 or includes the probe in the U. This U-shaped shim 123 couples the excitation from the neutralizing probe into the input cavity into the longitudinal field beyond the first quarter wavelength point. In this arrangement also, the penetration of the neutralizing probe 91, 97 into the input cavity 21 determines its proximity to the U-shaped shim 123 joining the two blocks 71, 72 and regulates the amount of the energy which is fed back from output to input.

The necessity for neutralization of the normal grounded grid amplifier arises from the fact that the output voltage between grid and anode is fed back between grid and cathode by means of the interelectrode capacitance between anode and cathode.

In addition to coupling back the energy from the output cavity into a longitudinal field in the input cavity, as shown in Figs. 7 and 8, or coupling that energy to a concurrent transverse field in the input cavity, as described in connection with the operation of the device of Figs. 1 through 4, an alternative neutralization arrangement will be described which utilizes the inductance of contact fingers engaging the control grid terminal 15 of the vacuum tube 11. The portion of the radio frequency output voltage which is fed back by means of the interelectrode capacitance of the vacuum tube 11 between the grid and cathode acts to additionally elevate the cathode above ground by the amount of the voltage drop across the inductive reactance of the cathode leads. By providing a grid terminal contacting ring having circularly spaced contacting fingers of the proper dimensions and spacing to provide an equivalent inductive voltage drop between the control grid and ground due to the feedback from anode to grid, the control grid electrode of the vacuum tube 11 is elevated above ground by the same amount as the cathode electrode due to the feedback of the output voltage by the interelectrode capacitances of the tube. This neutralization arrangement, utilizing circularly spaced contact fingers of the proper dimensions and spacing to produce an inductive reactance between an intermediate cavity resonator wall and the vacuum tube terminals is particularly described and claimed in the co-pending application of Thomas M. Gluyas, Ir., Serial No. 141,547, filed January 31, 1950.

One embodiment of the invention successfully tried out in practice was designed for the input cavity 21 to be operable over a range of frequencies from 235 to 890 megacycles and the output cavity 27 to be operable over a range of frequencies from 470 to 890 megacycles and had the following dimensions: The electron discharge device 11 was a type 6161 ultrahigh frequency power triode. The first or cathode wall 23, the intermediate or grid wall 25, and the third or anode wall 29 were made of %2 inch brass, silver-plated to reduce electrical losses. The spacing between the first or cathode wall 23 and the intermediate or grid wall 25 was inch. The spacing between the intermediate wall and the third or anode wall 29 was 1 inches. The shorting bars 31 in the input cavity 21 were inch high, "71 inch thick and 7% inches long, and carried in the channels therein springs 119 of a closely wound helical configuration made of silver-plated Phosphor bronze wire 0.015 inch in diameter, the diameter of the helix being inch. These helical springs 119 were subjected to inch nominal compression both top and bottom, a total of A inch compression in a direction normal to the input cavity walls 23, 25. The maximum distance between the shorting bars 31 was 9% inches, and the minimum distance to which they were adjustable was approximately 2% inches. The blocks 71 and 73 were also of silver-plated brass and had a length in the longitudinal direction of the cavity of A: inch, were 3 inches long in the transverse dimension, and were inch high, equal to nominal cavity wall spacing, but the blocks 71, 72 do not touch the intermediate wall 25.

The shorting bars 33 in the output cavity had the same thickness and length as the shorting bars 31 in the input cavity, but had a height of 1 inch. The contacting springs 109 in the channel in the shorting bars 33 were identical to those used in the input cavity 21 and were also subjected to inch nominal compression both top and bottom, a total of inch compression. The rectangular metallic block 41 in the output cavity 27 was of silver-plated brass and had a length of 3 inches in the longitudinal direction of the cavity, was 2% inch wide, inch thick, and included a cylindrical hole 1% inches in diameter to receive the type 6161 vacuum tube. The spacing between the rectangular block 41 and the anode wall 29 was /8 inch. The anode contacting ring 35 and the grid terminal contacting ring 39 were helical springs identical to those used in the shorting blocks 31 and 33; while the cathode terminal contacting ring 51 was a helix made of the same wire, but having a inch diameter rather than a /4 inch diameter like the others. The neutralizing probe 91 had a diameter of inch, while the disc 97 carried thereby had a diameter of Ms inch and a thickness of A; inch. The input and output coupling arrangements included short sections of coaxial lines 73, 74 and 81, S3 in which the inner conductors 74, 83 were of silver-plated brass rod 7 inch in diameter, and the inside dimension of the outer conductors 73, 81 was /4 inch. The discs 75, 35 were each 1% inch in diameter and inch thick.

What is claimed is:

1. In a high frequency system, an electron discharge device having a cathode, an anode, and a control grid, a cavity resonator structure for said device including separate input and output rectangular cavity resonators, said cavity resonator structure being defined by three flat parallel plates having registered apertures therein to receive said electron discharge device, the first of said plates being coupled to said cathode, the second of said plates being coupled to said grid and together with said first plate defining said input cavity, the third of said plates being coupled to said anode and together with said second plate defining said output cavity, whereby said second plate constitutes a common wall between said separate cavity resonators, a metal block having a thickness equal to or greater than the major portion of the spacing between said first and second plates and positioned in said input cavity adjacent said apertures.

2. In a high frequency system, an electron discharge device having a cathode, an anode, and a control grid, a cavity resonator structure for said device including separate input and output rectangular cavity resonators, said cavity resonator structure being defined by three flat parallel plates having registered apertures therein to receive said electron discharge device, the first of said plates being coupled to said cathode, the second of said plates being coupled to said grid and together with said first plate defining said input cavity, the third of said plates being coupled to said anode and together with said second plate defining said output cavity, whereby said second plate constitutes a common wall between said separate cavity resonators, a pair of metal blocks having a thickness equal to or greater than the major portion of the spacing between said first and second plates, said blocks being electrically coupled to one of said first two plates, and being positioned in said input cavity on opposite sides of and adjacent said apertures.

3. In a high frequency system, an electron discharge device having a cathode, an anode, and a control grid, a cavity resonator structure for said device including separate input and output rectangular cavity resonators, said cavity resonator structure being defined by three flat parallel plates having registered apertures therein toreceive said electron discharge device, the first of said plates being coupled to said cathode, the second of said plates being coupled to said grid and together with said first plate defining said input cavity, the third of said plates being coupled to said anode and together with said". second plate defining said output cavity, whereby said second plate constitutes a common wall between said separate cavity resonators, a metal block having a thickness equal to or greater than the major portion of thespacing between said second and third plates and having; an aperture therein to receive said electron discharge device, said block being positioned in said output cavity with the aperture in said block in registry with said aper-- tures in said plates and being electrically coupled to one: of said second and third plates.

4. In a high frequency system, an electron discharge: device having a cathode, an anode, and a control grid, a cavity resonator structure for said device including sep-- arate input and output rectangular cavity resonators, saidv cavity resonator structure being defined by three flat paral-- lel plates having registered apertures therein to receive: said electron discharge device, the first of said plates being; coupled to said cathode, the second of said plates beingcoupled to said grid and together with said first plate de fining said input cavity, the third of said plates being. coupled to said anode and together with said second plate defining said output cavity, whereby said second plate: constitutes a common wall between said separate cavity' resonators, said input cavity including a pair of metal. blocks having a thickness equal to or greater than the major portion of the spacing between said first and second plates, said blocks being electrically coupled to one of said first two plates and being positioned in said input cavity on opposite sides of and adjacent said apertures, said output cavity including a further metal block having a thickness equal to or greater than the major portion of the spacing between said second and third plates and having an aperture therein to receive said electron discharge device, said further block being positioned in said output cavity with the aperture in said block in registry with said apertures in said plates, and being electrically coupled to one of said second and third plates.

5. An amplifier system comprising rectangular shaped cavity resonator input and output circuits arranged adjacent each other, apertures in said resonators in the center portions thereof registering with each other, an electron discharge device mounted in said apertures and penetrating both of said resonators, said input resonator being tuned to three-quarter wave resonance at the operating frequency, said output resonator being tuned to onequarter ,wave resonance at the operating frequency, each of said'cavity resonator circuits containing metal blocks adjacent said apertures and occupying the major-portion of the spacing between, opposed surfaces in said resonators,-said blocks in said input resonator being located more than one-quarter but lessthan one-half of an effective wavelength atthe operating frequency from the electrodes of said electron discharge device, and an .adjustable feedback probe coupling said output resonator to the second quarter wavelength portion of said input resonator. V

6. Input and output circuits for a vacuum tube comprising, box-like input and output cavity resonator structures formed by three parallel spaced rectangular metallic plates and metallic side and end walls, the intermediate one of said three parallel plates constituting a common wall for the input cavity on one side and the output cavity on the other side, said end walls being arranged for sliding contact with the corresponding plates and side walls to vary the longitudinal dimensions of the cavities and thereby vary the frequency at which the cavities are resonant, said parallel rectangular plates being provided with registered apertures having edges adapted for coupling to electrode contact rings of a vacuum tube, and conductive blocks in said cavities adjacent said apertures to constitute sections of low impedance line interposed in the longitudinal direction between the vacuum tube and the remainders of the cavity resonators.

7. A box-like cavity resonator structure for use as an input or output circuit for a vacuum tube comprising, two

. 12 parallel spaced rectangular plates, side walls connecting said plates, end walls arranged for sliding contact with said plates and side walls to vary the longitudinal'dimen? sion of the cavity and thereby vary the frequency at which the cavity is resonant, said cavity constituting a waveguide line extending from one end wall to the other end wall and having a characteristic impedance determined in part by the spacing of said parallel plates, said parallel rectangular plates being provided with registered apertures having edges adapted for coupling to electrode contact rings of a vacuum tube, and conductive means between saidparallel plates and spaced from at least one of said plates, said conductive means being located'ad jacent to said apertures to provide sections of lineextending in the longitudinal direction and having a much lower impedance than said characteristic impedance. 8. An input circuit. and an output circuit for a vacuum tube comprising, two box-like cavity resonator structures as defined in claim 7 arranged adjacent to each other with said apertures in said plates in register with each other to receive a single vacuum tube.

References Cited in the file of this patent V UNITED STATES PATENTS I Lafferty July 1, 1947 

